Handheld QKD

The infrastructure for quantum key distribution is being developed in satellite and fiber communications to protect against future hackers with quantum computers. But what about our everyday transactions?

Quantum Security in the Palm of Your Hand

Researchers at the Ludwig Maximilian University in Munich have developed a handheld device prototype combining micro-optics with easily integrable electronics to equip future mobile devices with quantum key exchange technology. In such a device, credit card information can be transmitted to a receiver at an ATM or point-of-sale with proven security against any interceptor. The device makes use of four different orientations of the polarization of light ranging from vertical, horizontal, diagonal, and anti-diagonal, and each leading to a bit of either 1 or 0.

In the sender, spatial overlap at high modulation rates is achieved by sending weak laser pulses from four different diodes through their respective polarizer filter and into a waveguide that leads all four inputs to a single output. The security of the protocol is ensured when polarization states are perfectly unpredictable and when no possible measurements by an interceptor can help predict the outcome of bits. The wavelength, spatial form of the beam, and time between pulses must give no hint of which bit may be produced.

Along with automatized optical alignment in the receiver, the micro-optics hardware and electronics have enabled a 30 kHz secure key rate.  Improvements in hardware and using a decoy state protocol of varying laser intensities will improve these results even further.